1. Field of the Invention
The present invention relates generally to a weighing system which incorporates hydraulic load cells, and more particularly to a hydraulic weighing system which includes a digitally compensated pressure transducer module so as to provide a more cost-effective, accurate, hydraulic weighing system.
2. Description of the Related Art
Weighing systems which incorporate hydraulic load cells are well-known in the art. A typical hydraulic load cell includes a piston which is mounted in a cylinder. The hydraulic load cell is mounted to a weighing platform such that the force applied to the weighing platform is transmitted to the piston, thereby compressing hydraulic fluid in the cylinder. Examples of hydraulic load cells are shown for example, in U.S. Pat. Nos. 3,658,143; 3,633,695; 3,646,854; 3,658,142; 4,360,071; 3,999,427; 3,889,529; 4,383,584; and 3,765,497.
One technique for measuring the load on the hydraulic load cell is to measure the pressure of the hydraulic fluid. An overview of a number of types of pressure transducers is provided in "Handbook of Transducers for Electronic Measuring Systems--Chapter 10, " H Norton, Prentice Hall, Inc. (1969). As for measuring the total weight on a weighing platform, Bradley, U.S. Pat. No. 3,992,946, relates to a weighing apparatus which comprises a plurality of load cells, each including a piston, a cylinder and a flexible diaphragm. The cylinders are interconnected in spaced coaxial relation on a support frame. An output signal is generated which combines the total output pressures of the independent hydraulic load cells.
Miller, U.S. Pat. No. 4,456,084 relates to a system for monitoring the load carried by a vehicle. A plurality of load cells extend between a load bed and the unsprung portion of the vehicle suspension. Each load cell includes a hydraulic cylinder which generates a hydraulic force corresponding to the load applied thereto. A pressure transducer is connected to each hydraulic cylinder, and the outputs of the transducers are summed and fed to an auto-zeroing system. The output of this system is connected to A.backslash.D converter and then to a visual display.
Huff, U.S. Pat. No. 5,117,373 relates to a weighing system that includes a hydraulic cell with an analog pressure transducer. The output of the pressure transducer is coupled with an A/D converter to convert the analog signal to a digital signal. The weight is conditioned by utilizing pressure and temperature amplification, which allow the container to be zeroed and scaled to monitor the weight.
Davis et al., U.S. Pat. No. 4,836,308, relates to a weighing system that includes hydraulic load cells and pressure transducers to generate an analog signal having an amplitude proportional to the weight on the load cells. A conversion device converts the analog signal into an oscillation signal having a frequency which is proportional to the weight on the platform. A counter couples to the conversion device to monitor the oscillation signal and to provide a monitored load count which is proportional to the weight. A computer converts the load count into a signal representative of the weight.
It is desirable to have a weighing system that provides the benefits of the use of multiple hydraulic load cells and which i) is relatively inexpensive to manufacture as compared to conventional strain gauge load cells; ii) is modular with components that may be used in weighing systems having different load ranges; and iii) provides digital compensation for errors in the system components so as to provide the accuracy required of a commercial scale. None of the aforementioned devices provides each of these benefits.